Electrical circuitry often must be protected from disruptions caused by electromagnetic interference (EMI) and radio frequency interference (RFI) entering the system.
In addition to protecting electronic equipment against EMI/RFI energy, there is also a need to protect the equipment against power surges owing to electrostatic discharges (ESD) and electromagnetic pulse (EMP). The high voltage generated by ESD and EMP can damage voltage sensitive integrated circuits and the like.
The present invention relates to data transmission systems for transmitting information between a master unit and one or more remote units of a subordinated system or between subordinated terminal units in systems known generally as local area network or wide area network systems. In interconnecting equipment in such systems it is necessary to both transmit and receive information from other members in the system. Generally, these systems use a coaxial connector comprised of an inner signal line and an outer shield member to filter interference from the line. Both the sending and receiving signal lines are interconnected by such coaxial connectors. This requires a plurality of coaxial transmission lines be established between various units within the system.
With the wide use of such systems, it is desirable to have a more cost effective system wherein one coaxial connector transmission line can be used as both the sending and receiving line. In such a system, the shield of the coaxial connector is used as a return line instead of a shield for the outgoing signal. The return line then is now an unshielded signal line and must be filtered to prevent spurious signals from entering the electronic equipment. It is necessary, therefore, to isolate the ground system of the equipment from the shield, now signal line, of the coaxial connector.
Generally, the isolation between the connector and ground is accomplished by the use of isolation bushings, one placed between the connector and the back panel of the equipment, and the second placed between the back panel and the mounting means used to mount the connector to the back panel of the equipment. Filtering between the connector and ground has been accomplished by the use of leaded capacitive devices connected between the outer shell of the coaxial connector and the ground system of the electronic unit such as a terminal, thus isolating AC current from the DC signal line and transmitting the AC current to ground. Since leaded devices have an extra impedance associated with the leads it is desirable to have a means for isolating the AC current that uses unleaded devices.
In many instances it is desirable to have an external filtering device that is an "add-on" device to provide filtering to an already existing non-filtered connector. This is particularly desirable in instances when the same basic connector may be used in a number of different applications, each having different filtering requirements. It is also desirable that a method of making the devices be found to that will lend itself to automation of the assembly line by robotic devices and the like that will enable filtered connectors to be manufactured in a more cost effective manner.